The Impact of Urbanization on Mesoscale Convective Systems in the Yangtze River Delta Region of China: Insights Gained From Observations and Modeling

Urbanization is an important factor that may influence the formation and development of clouds and precipitation. In this study, we focus on studying the influence of urbanization on mesoscale convective systems (MCS) over the Yangtze River Delta region in China under different synoptic conditions using a combination of radiosonde, meteorological station, and satellite observations. It demonstrates that synoptic forcing can be used to distinguish the effect of land cover and land use on MCS. When the synoptic-scale forcing is weak, the urban heat island (UHI) is the main factor affecting the vertical development of clouds. The UHI decreases atmospheric stability and enhances horizontal convergence, invigorating clouds over and downwind of cities. On the other hand, when strong synoptic-scale forcing is present, buildings in cities cause clouds to bifurcate upwind of cities, moving around them, primarily through their dynamic effects. The heights of cloud tops in central and downwind parts of cities thus drop. Using the Weather Research and Forecasting model simulations of different atmospheric forcings also demonstrate similar patterns around major urban areas. The joint analyses of observations and model simulations provide new insights into the net effects of urbanization on cloud systems.